Thurman/Ugas makes way more sense
Actually it doesn't anymore because of the likelihood of Ugas being demoted back down to regular champion.
Keith has said he wants his next fight to put him in line for a title shot. When he was asked if he would fight Jamal James (who is the current regular WBA champ) he said it wouldn't make sense because it he wouldn't be a real champ, and he knows the WBA never makes the Super champion fight the regular champion. So him beating James would only leave him deadlocked. Swap James with Ugas, and it's the same thing.
Fighting Porter makes more sense for Thurman because Porter is ranked #1 in the WBC rankings. And Thurman himself is ranked 3rd. So beating Porter would put him #1 and Keith can make himself a mando.
I'm surprised Porter would take this fight, because he has more to lose than gain fighting Keith. As of now, he's 1st in line to get a shot at the title. If he loses to Thurman then he'll lose his opportunity as well. Maybe he thinks Keith's long layoff gives him the advantage